Meeting Abstract
The diversification of bird flight involved major changes to the pectoral girdle and musculature, including modification of the furcula. The furcula articulates with the scapulo-coracoid complex medially to the glenoid and is the rostral-most attachment of m. pectoralis, the primary downstroke muscle in flying birds. As a result, furcula morphology has been used to infer flight behavior in extinct avialans. However, furcula morphology only modestly correlates with flight style in extant birds, and some volant birds lack furculae. While furcular morphology has often been considered in isolation – under the assumption that the functional signal of the element resides in its gross shape – the bone’s anatomical orientation, structural properties, and relation to adjacent pectoral muscles remain unexplored in most avians. We collected contrast imaging, dissection, and morphometric data of the musculoskeletal system from nine passerines (Passeriformes) and parrots (Psittaciformes), groups with disparate furcula morphology but similar flight styles. Generally, passerines possess more robust and rostrocaudally-curved furculae than do parrots, whose furculae are reduced to ligamentous bands in some taxa. We examined pectoral muscle architecture, muscle resultants, and mechanical properties of the furcula as correlates of flight style and furcular morphology. In volant parrots with reduced or absent furculae, modified pectoral muscle architecture and morphology may functionally replace a bony furcula. Whereas earlier studies found that lateral and anterior furcula shape may covary with flight style among all avians, we find that these trends may not hold at higher taxonomic resolution. Our data suggest that the question of furcula function, and thus of avian pectoral evolution, depends on taxonomic level.
